A method and device for cost-optimised control of a regenerable filter in a water circuit of a heat exchanger.
The present invention relates to a method for cost-orientated control of a regenerable mechanical filter, in particular for contaminants in the cooling water flow preceding heat exchangers, with:
a filter arranged between the cooling water pump and heat exchanger in the path of the cooling water supply line, with a filter housing, at least one filter element covering the cross-section of the housing, at least one cleansing device acting upon the filter element and flushing away the contaminants, and at least one flush water line which can be connected to a flushing means and is used for removal of the contaminants flushed out, PA1 at least one or more sensor(s) monitoring the operating condition of the installation, the signal lines of which output signals (S1, S2 . . . Sn) which indicate the operating condition of the whole installation composed of a cooling water pump, filter and heat exchanger, impaired by the fouling of the filter, PA1 a flush command generator which is connected on the one hand with the signal lines providing the signal (S1, S2 . . . Sn) and on the other hand, on its command line, makes the flush command (Sa) for flushing the filter switchable, PA1 a flushing process control, which is connected to the command line of the flush command generator, so that when there is a switch position signalling the flush command, the command line makes the flushing process practicable by opening the flushing means and by actuation of the cleansing device. PA1 when a flush point is set high in order to obtain little filter flushing, high power losses through filter fouling occur, PA1 the other hand, however, with a flush point set low to obtain a low power loss through filter fouling, frequent filter flushing with correspondingly high power losses can occur. PA1 a. sensing at least one measured value, from which a current degree of fouling of the filter (5) can be deduced, and supplying the value to a flush command generator (14); PA1 b. calculating by at least one functional correlation stored in the flush command generator (14), in pre-determined time intervals respectively a first (.DELTA.N1) and a second (.DELTA.N2) power loss, wherein PA1 c. determining from the development over time of the first calculated power loss (.DELTA.N1) respectively the total energy losses (.DELTA.E1) caused as a whole by the fouling of the filter since the last regeneration; PA1 d. calculating a current second energy loss (.DELTA.E2) respectively for a flushing procedure which comprises the second power loss multiplied by the duration of the regeneration (.DELTA.T2); PA1 e. adding the current calculated second energy loss (.DELTA.E2) to the respective current total energy loss (.DELTA.E1) accumulated, and dividing the sum by the time elapsed (.DELTA.T1) since the last regeneration inclusive of the time (.DELTA.T2) needed for a regeneration procedure; PA1 f. monitoring the development over time of these quotients ([.DELTA.E1+.DELTA.E2]/[.DELTA.T1+.DELTA.T2]) and triggering a regeneration procedure when the quotient has passed through a minimum and is increasing again. PA1 a flush command generator (14) with an input unit (20) and non-volatile memories (22) for functional correlations of parameters, PA1 at least one sensor (12; 18; 19) for receiving measured values from which, at predetermined intervals, respectively a first power loss (.DELTA.N1) which is caused by the fouling of the filter can be calculated as a change in output of the cooling water pump (4) and as a change in output of the heat exchanger (1), PA1 means (23) for calculating of the total energy loss (.DELTA.E1) calculated from the development over time of the first power losses (AN I) since the last regeneration of the filter (5), PA1 means (23) for calculating the current energy loss (.DELTA.E2) to be expected to be caused by a regeneration procedure as a change in output in the cooling water pump (4) and as a change in output of the heat exchanger (1), PA1 means (23) for recognising when the current sum of the total energy loss (.DELTA.E1) and of the energy loss (.DELTA.E2) expected with a regeneration divided by the time since the last regeneration inclusive of the regeneration time (.DELTA.T1+.DELTA.T2) to be expected has reached a minimum or has exceeded it, and for triggering a regeneration process resulting from this.
Installations of this type have been known for a long time. Thus, an installation of the known type is described in the publication by A. Lange entitled "Kosteinsparungen durch verbesserten Betrieb der Kuhlrohr-Reinigungsanlage, Einsatz von Kuhlwasserfiltem und einer neuartigen Kondensatoruberwachung" [Cost savings by improved operation of cooling tube cleaning installations, use of cooling water filters and novel condenser monitoring] in VGB Kraftwerkstechnik 70 (1990), Volume 8, pages 681 to 688. The filter is installed in the cooling water supply line preceding the heat exchanger, in this case a turbine condenser for condensing the vapour leaving a turbine. The cooling water pump necessary for the process is arranged upstream of the filter, but is not shown. The filter has a filter element, called the filter insert, covering the housing cross-section, a cleansing device acting upon some areas of the filter element and flushing out the contaminants, called a rotor, with rotor drive, and a flush water line penetrating the walls of the housing, which is connected downstream of the heat exchanger to the cooling water drainage line and can be connected to a waste water means, called a flushing means, and is for removal of the flushed out contaminants.
The filter installation has a sensor monitoring the operating condition of the installation, described as a pressure differential measurement system, the signal line of which provides an electrical signal which indicates the increased pressure differential of the filter caused by the fouling of the filter and thereby the impaired operating condition of the whole installation composed of a cooling water pump, filter and heat exchanger.
A flush command generator, which on the one hand is connected to the signal line of the sensor providing the signal and on the other hand transmits the flush command for flushing the filter to a flush process controller for opening the flushing means and actuating the cleansing device, is combined together with the flush process control in a unit described as a control cabinet.
The control of the installation is done in that the pressure differential measuring system monitors the degree of fouling of the filter means. If a pressure differential of the filter, measured by the pressure differential system, reaches a set limit value, the flush command generator provides the flush command to the flush process control, which switches on the rotor drive and opens the waste water means.
A further embodiment of the known control of the installations of the known type described is described in Japanese document 61-38000. The filter element is in this case cylindrical and is composed, for example, from perforated sheet metal. The cleansing device is a regulator flap arranged directly in front of the filter inlet, which, during filter flushing produces a high-speed turbulent ring flow, by means of which the contaminant particles are lifted from the filter element and transported to the flush water line. The installation has a pressure differential measuring system as the sensors monitoring the operating condition of the installation, and a cooling water volume flow measuring system, the signal lines of which provide electrical signals which indicate the impaired operating state caused by the fouling of the filter of the whole installation composed of a cooling water pump, filter and heat exchanger. The flush command generator is composed of a function memory and a comparator and is connected to the signal lines of the pressure differential measuring system and of the cooling water volume flow measuring system. The flush process control is connected to the command line of the flush command generator. The method for controlling the installation is that in the comparator the current pressure differential of the filter is compared with a set value dependent on the cooling water volume flow pre-determined in the function memory, and when the set value is exceeded the flush command for flushing the filter is given electrically to the flush process control, which in turn initiates filter flushing by opening the flushing means and actuation of the regulator flap.
Installations also belong to the prior art in which the flush water line is not connected to the cooling water drain line, but instead to an open waste water channel or a waste water store. The filter element can be configured in very different ways, for example extending in a two-dimensional manner as a so-called surface filter (for example made from stamped, perforated sheet metal and formed as a planar surface or cylinder or spherical cup) or as a so-called deep-bed filter composed, for example, of wound thread or from a pile of sand or activated charcoal. The cleansing device can be a back flush rotor, as in the described publication by A. Lange, a regulator flap as in the described Japanese publication 61-38000, or also be composed of several shut-off flaps, with the aid of which parts of the filter element are separated one after another from the flow of cooling water on the inlet side and are connected to the flush water line, wherein there is a back flushing with cleansed cooling water, from the filter outlet through the filter element, of the part of the filter element shut off. The filter housing can also be composed of several individual housings which can be separated from the common cooling water supply line one after another by means of shutting-off means at the filter inlet for flushing, and can be connected to a common flush water line by means of flushing means. The present invention shall relate to all regenerable mechanical filters for liquids known per se, described and not described, and not be limited to cooling water installations.
Apart from the fact that it is also known to generate the flush command manually by means of a push button or by means of a timer, it is common to the known methods for controlling a regenerable mechanical filter that the flush command for flushing the filter is generated when the pressure differential of the filter or of the filter element, measured by a pressure differential measuring system, exceeds a limit value or, in an improved embodiment, a limit value pre-determined in fixed dependency upon the current cooling water volume flow, wherein the cooling water volume flow can be measured with different types of sensors.
The pressure loss of the filter insert increases because of the fouling of said filter means with contaminants from the flow of cooling water. In the case of cooling water pumps with an unregulated drive this causes a reduction in the cooling water volume flow, which causes a reduced thermal output at the heat exchanger. In the case of cooling water pumps with a regulated drive, or with blade adjustment, this can partly be compensated for by increased pump output. As a whole, the fouling of the filter means causes reduced efficiency of the whole installation composed of a cooling water pump, filter and heat exchanger, which is indicated by the pressure differential measuring system and possibly by the cooling water volume flow measuring system, being the sensors monitoring the operating condition of the installation, and is described as the "power loss through filter fouling". The filter should therefore be flushed when there is as little fouling of the filter means as possible, and therefore as often as possible in order to obtain as little average power loss through filter fouling as possible.
However, when the fouled filter is flushed, the cooling water volume flow supplied to the heat exchanger is reduced by the amount of the flush water flow. The corresponding thermal effect is lost by the heat exchanger. Overall, the filter flushing causes impairment to the efficiency of the whole installation composed of the cooling water pump, filter and heat exchanger which is described as the "power loss through filter flushing". The filter should therefore be flushed as little as possible in order to obtain a low power loss through filter flushing.
With the known methods for controlling the installations described for the mechanical cleaning of liquids, it is disadvantageous that:
With frequent filter flushing the correspondingly high actuating energy and the rapid wearing out of the cleansing device and of the flush water means are disadvantageous.
The disadvantage of the known device is thus essentially that the flush point is set in a fixed manner or in fixed dependency upon the cooling water volume flow, and this does not take into consideration the periodically varying concentration of the contaminants in the cooling water flow, and thereby when there is low contamination a disproportionately high "power loss through filter fouling" occurs and when there is high contamination a disproportionately high "power loss through filter flushing" occurs. Taken as a whole, it is disadvantageous that the determination of the flush point takes place as a rule according to technical standpoints and not according to possibly changing energy criteria and economic criteria associated with these.